1. Field of the Invention
The present invention relates to a method for making hydrophobically associative polymers (HAPs) using a brine dispersion method, and to compositions including these polymers.
2. Description of Background and Other Information
HAPs have been extensively studied in both academia and industry. The highly associative structure of a HAP in aqueous media results in its unique rheological properties, salt resistance and extremely high solution viscosity, which are very desirable in many applications, such as enhanced oil recovery, thickening and drug release applications.
U.S. Pat. Nos. 4,432,881 and 4,528,348 teach a micellar polymerization method for making polyacrylamide-based associative polymers by copolymerizing a hydrophobic comonomer with acrylamide or acrylic acid in aqueous solution in the presence of surfactants. The method has a severe disadvantage because the highly associative behavior of a HAP results in an extremely high bulk process viscosity, which causes difficulties in agitation and leads to incomplete monomer conversion. The high solution viscosity of HAP also leads to gel like final product appearance, and makes it very hard to transport and handle. Furthermore, the high process viscosity also limits the initial monomer concentration that could be used for the polymerization, which results in a final polymer having lower Molecular Weight (MW) and lower active content compared to the polymers made by emulsion and dispersion polymerization methods. Therefore, micellar polymerization is not a desirable method for large-scale production of HAP polymers.
U.S. Pat. Nos. 4,524,175 and 4,521,580 also teach, respectively, a HAP production method by water-in-oil emulsion and a HAP production method by microemulsion. However, the methods result in a product containing a significant amount of oil and surfactant which is undesirable for some applications and may cause increasing environmental concern as well as the inconvenience and expense associated with the make-down equipment for feeding the emulsions.
U.S. Pat. No. 5,707,533 teaches a brine dispersion polymerization method for preparing high molecular weight polyacrylamide copolymers comprising polymerizing a cationic monomer and an N-alkylacrylamide or an N,N-dialkylacrylamide in an aqueous salt solution. However, the associative properties of the polymers and the surfactant addition as described in the present invention is not disclosed in the ""533 patent.
The present invention is directed to a method for producing HAPs by a brine dispersion polymerization method. Highly associative anionic HAP with its MW larger than 1,000,000 Dalton is synthesized in an aqueous salt solution. The HAP final product with a homogenous particle dispersion form has a bulk viscosity below 3000 cp.
The present invention relates to a method for producing a HAP which includes forming a monomer solution containing surfactant, at least one hydrophobic ethylenically unsaturated monomer, at least one hydrophilic monomer selected from nonionic ethylenically monomers, cationic ethylenically unsaturated monomers, anionic ethylenically unsaturated monomers or mixtures thereof, and water; forming a salt solution containing multivalent salt, stabilizer and water; mixing the monomer solution and the salt solution to form a mixed solution; and charging the mixed solution with an initiator, thereby polymerizing the monomers to form the HAP. The method may further include adding from about 0.01 to about 0.5 grams of free radical initiator per 100 grams of the total monomer.
The monomer solution may be formed by mixing the at least one hydrophilic monomer and water to form a monomer solution, adding the at least one hydrophobic ethylenically unsaturated monomer and surfactant to the monomer solution, and mixing until homogeneous.
The salt may be present in an amount of up to about 50% by weight, or preferably from about 10% to about 30% by weight, of the salt solution. The stabilizer may be present in an amount of up to 10% by weight of the salt solution, preferably in an amount from about 0.05% to about 2% by weight and more preferably in an amount from about 0.1% to about 0.5% by weight. A preferred stabilizer may be chemically modified quar gum.
The surfactant may be present in an amount up to about 10% by weight of the monomer solution, preferably in an amount from about 0.1% to about 2% by weight, and more preferably in an amount from about 0.25% to about 1% by weight. A preferred surfactant is sodium dodecyl sulfate.
The HAP is preferably a copolymer of acrylic acid, acrylamide, and lauryl acrylate.
The present invention also relates to a method for producing a HAP which includes: mixing at least one hydrophilic monomer selected from nonionic ethylenically monomers, cationic ethylenically unsaturated monomers, anionic ethylenically unsaturated monomers or mixtures thereof and water to form a monomer solution; adding at least one hydrophobic ethylenically unsaturated monomer and surfactant to the monomer solution and mixing until homogeneous; forming a salt solution comprising multivalent salt, stabilizer and water; mixing the monomer solution and the salt solution to form a mixed solution; and charging the mixed solution with an initiator to polymerize the monomers to form the HAP.
The present invention also relates to a method for producing a water soluble HAP containing acrylic acid, acrylamide, and lauryl acrylate, wherein the method includes forming a monomer solution of acrylic acid, acrylamide, lauryl acrylate, an anionic surfactant, and water; forming a salt solution comprising multivalent salt, stabilizer and water; mixing the monomer solution with the salt solution to form a mixed solution; and adding an initiator to the mixed solution, thereby polymerizing the acrylic acid, the acrylamide and the lauryl acrylate to produce a dispersion containing the water soluble HAP.
The present invention also relates to a method for producing a hydrophobically associative polymer which includes:
forming a monomer solution comprising up to about 10% by weight of surfactant, at least one hydrophobic ethylenically unsaturated monomer, at least one hydrophilic monomer selected from nonionic ethylenically monomers, cationic ethylenically unsaturated monomers, anionic ethylenically unsaturated monomers or mixtures thereof, and water;
forming a salt solution comprising up to about 50% by weight of multivalent salt, up to 10% by weight of stabilizer and water, the weight percent being based on the total weight of the salt solution;
mixing the monomer solution and the salt solution to form a mixed solution; and
charging the mixed solution with from about 0.01 to about 0.5 grams of free radical initiator per 100 grams of the total monomer content, thereby polymerizing the monomers to form the HAP.
The present invention also relates to an aqueous dispersion comprising the HAP made by any of the foregoing methods. The aqueous dispersions have many uses. The aqueous dispersion containing the HAP may be used as the one or more retention and drainage aids in a papermaking process from pulp furnish or as the one or more thickeners in a paint formulation containing pigment, polymer and a thickener.
The aqueous dispersion containing the HAP may be used as the one or more thickening agents in a mobility control fluid useful in enhanced oil recovery operations or as the one or more fluid loss control additives in a hydraulic cementious composition.
The aqueous dispersion containing the HAP may be used as the one or more viscosification agents either in an oil well drilling mud formulation for oil field production or in an oil well completion fluid.
The aqueous dispersion containing the HAP may also be used in a fracturing fluid formulation in oil recovery.
The aqueous dispersion containing the HAP may be used as the one or more flocculation aids in a waste water treatment system or in a dewatering sludge system.
The aqueous dispersion containing the HAP may be used as the one or more rheology controls in a secondary or tertiary oil recovery system.
The aqueous dispersion containing the HAP may be used as the one or more mobility control agents in an enhanced oil recovery method which includes forcing an aqueous flooding medium containing one or more mobility control agents from an injection well through a subterranium formation toward a producing well.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.
The inventive method can successfully polymerize a hydrophobic comonomer with one or more hydrophilic comonomers to produce a high molecular weight HAP. An important advantage of the present method over the existing micellar polymerization process is its ability to avoid high viscosity during polymerization and to provide complete monomer polymerization with an attendant high active content in the HAP. These advantages make this an ideal method for production scaleup. Moreover, the resultant HAP is in an aqueous homogeneous dispersion, which does not contain any oil, and is highly desirable in a papermaking process, and may be used without further processing, because the salt in the dispersion will not affect the papermaking process. In papermaking, the dispersion may be diluted with water on site and caustic may be added to neutralize the dispersion, if desired.
The make-down process of this dispersion, i.e., the dilution of the dispersion, is easier as compared to the prior art emulsion products, which contain oil. The resulting HAP is highly associative in aqueous solution as indicated by its viscosity and viscoelasticity, which sets it apart from conventional high molecular weight dispersion products.
If the end user desires to remove the salt from the dispersion, the salt may be removed by using a conventional dialysis method.
The aqueous dispersion containing the HAP is a concentrate, which can be diluted by the end user to meet the end user""s particular needs. For example, the aqueous dispersion containing the HAP may used as thickening agents for paint formulations or for personal care applications.
The aqueous dispersion containing the HAP can be used as retention and drainage aids for papermaking process as illustrated in the examples. Furthermore, the aqueous dispersion containing the HAP may be used as clarifying agents and flocculation aids for water and wastewater treatment and for sludge dewatering. The aqueous dispersion containing the HAP can also be used as a binder for non-woven materials or in waterborne adhesives. The aqueous dispersion containing the HAP may be used in water-based inks.
The aqueous dispersion containing the HAP may be used as a fluid loss control additive in hydraulic cement compositions, i.e., inorganic cements that harden or set under the influence of water. These compositions are frequently used in cementing operations associated with oil, gas, water and brine wells, as well as dam and tunnel construction. For example, aqueous hydraulic cement slurries are used during or after the completion of the drilling of an oil or gas well to fill the annulus between the borehole and the outside of the casing. In some cases, the borehole is in porous strata and the water in the hydraulic cement composition may flow out of the slurry into the porous strata. As a consequence, the cement composition may not properly cure. To prevent the fluid loss, a fluid loss control additive is added to the cementious composition.
In oil field production, the aqueous dispersion containing the HAP may be used in a drilling mud formulation, in an oil well completion fluid, in an oil field work fluid, in a fracturing fluid formulation in oil recovery, or as a thickening agent in a mobility control fluid useful in enhanced oil recovery operations. The dispersion may be used as a rheology control for secondary or tertiary oil recovery.
The present method for making the HAP includes the following steps:
1) forming a monomer solution of one or more of nonionic monomer, anionic monomer and cationic monomer in distilled water,
2) forming a solution of hydrophobic monomer with a surfactant,
3) mixing the two solutions until a homogeneous monomer solution is formed,
4) preparing a brine solution comprising distilled water, multi-valent salt and stabilizer,
5) mixing the solution of step 3 with the brine solution of step 4 and charging the mixed solution to a reaction kettle, and
6) polymerizing the solution to produce the HAP in a dispersion.
The order of mixing is not critical to the inventive method as long as the resultant mixture is a solution or a homogeneous dispersion. For example, the monomer solutions of both hydrophilic monomers and hydrophobic monomers can be formed in one step or in multiple steps without regard to the order of the steps. Likewise, depending upon the conditions, the skilled worker may mix the brine solution with the various monomers at the same time. The monomers, surfactants, polymerization initiators and initiator burnout to be utilized are conventional materials known in the art to the skilled artisan. The method and materials to be utilized are explained in more detail below.
The HAP is preferably a copolymer comprising hydrophobic groups that are capable of forming physical network structure through hydrophobic association, and at least one monomer selected from the group consisting of nonionic ethylenically unsaturated monomers, cationic ethylenically unsaturated monomers, and anionic ethylenically unsaturated monomers. Further, as a matter of preference, the indicated monomers of the water-soluble hydrophobically modified polymer comprise at least one hydrophobic ethylenically unsaturated monomer, at least one anionic ethylenically unsaturated monomer, and at least one nonionic ethylenically unsaturated monomer. As a matter of particular preference, the at least one hydrophobic ethylenically unsaturated monomer comprises a monomer selected from the group consisting of C8-C20 alkyl esters or amides of ethylenically unsaturated monomer, while the at least one anionic comprises at least one member selected from the group consisting of acrylic acid, methacrylic acid, and their salts, and the at least one nonionic ethylenically unsaturated monomer comprises at least one member selected from the group consisting of acrylamide and methacrylamide. The preferred polymer will have a dynamic oscillation frequency sweep tan xcex4 value below 1.
Suitable HAPs include copolymers comprising at least one hydrophobic ethylenically unsaturated monomer. These copolymers further include at least one nonionic ethylenically unsaturated monomer, and/or at least one cationic ethylenically unsaturated monomer, and/or at least one anionic ethylenically unsaturated monomer. The HAP may include copolymers of methacrylic or acrylic acid, acrylamide or methyl acrylamide and lauryl acrylate or lauryl methyl acrylate.
As a matter of preference, the proportion of hydrophobic ethylenically unsaturated monomer in the HAP is within a range which renders the polymer water soluble hydrophobically associativexe2x80x94i.e., the hydrophobic monomer concentration is low enough so that the polymer is still water soluble, but sufficient to provide the associative property as discussed herein. In this regard, the HAP of the invention preferably comprises about 0.001 mole percent to about 10 mole percentxe2x80x94more preferably about 0.01 mole percent to about 1 mole percent, and still more preferably about 0.1 mole percent to about 0.5 mole percentxe2x80x94hydrophobic ethylenically unsaturated monomer.
The HAPs of the invention include anionic, nonionic, and cationic and amphoteric copolymers. Of these, the anionic copolymers are preferred.
The anionic copolymers comprise at least one hydrophobic ethylenically unsaturated monomer and at least one anionic ethylenically unsaturated monomer. Preferably, the anionic copolymers further comprise at least one nonionic ethylenically unsaturated monomer. Particularly preferred are the terpolymers consisting of, or consisting essentially of or substantially of, at least one hydrophobic ethylenically unsaturated monomer, at least one anionic ethylenically unsaturated monomer, and at least one nonionic ethylenically unsaturated monomer.
For the anionic copolymers, the preferred hydrophobic ethylenically unsaturated monomers are the hydrocarbon esters of xcex1,xcex2-ethylenically unsaturated carboxylic acids and their salts, with dodecyl acrylate and dodecyl methacrylate being particularly preferred. Preferred nonionic ethylenically unsaturated monomers are acrylamide and methacrylamide. Preferred anionic ethylenically unsaturated monomers are acrylic acid and methacrylic acid.
The anionic copolymers preferably comprise about 0.001 mole percent to about 10 mole percent hydrophobic ethylenically unsaturated monomer, about 1 mole percent to about 99.999 mole percent nonionic ethylenically unsaturated monomer, and about 1 mole percent to about 99.999 mole percent anionic ethylenically unsaturated monomer. More preferably, they comprise about 0.01 mole percent to about 1 mole percent hydrophobic ethylenically unsaturated monomer, about 10 mole percent to about 90 mole percent nonionic ethylenically unsaturated monomer, and about 10 mole percent to about 90 mole percent anionic ethylenically unsaturated monomer. Still more preferably, they comprise about 0.1 mole percent to about 0.5 mole percent hydrophobic ethylenically unsaturated monomer, about 50 mole percent to about 70 mole percent nonionic ethylenically unsaturated monomer, and about 30 mole percent to about 50 mole percent anionic ethylenically unsaturated monomer.
Preferred anionic HAPs include:
1) polymers comprising about 50 mole percent of acrylic acid, about 0.1 to about 0.5 mole percent of lauryl methacrylate and about 49.9 to about 49.5 mole percent of acrylamide;
2) copolymers comprising about 50 mole percent of acrylic acid, about 0.1 to about 0.5 mole percent of lauryl acrylate and about 49.9 to about 49.5 mole percent of acrylamide;
3) copolymers comprising about 50 mole percent of methacrylic acid, about 0.1 to about 0.5 mole percent of lauryl methacrylate and about 49.9 to about 49.5 mole percent of acrylamide; and
4) copolymers comprising about 50 mole percent of methacrylic acid, about 0.1 to about 0.5 mole percent of lauryl acrylate and about 49.9 to about 49.5 mole percent of acrylamide.
The HAP of the invention preferably has a weight average molecular weight of about 10,000 to about 10,000,000. This polymer more preferably has a weight average molecular weight of about 100,000 to about 5,000,000, and still more preferably about 500,000 to about 3,000,000.
Size Exclusion Chromatography (SEC) is used to determine weight average molecular weight. A dilute solution of polymer, typically 2% or less, is injected into a packed column. The polymer is separated based on the size of the dissolved polymer molecules and compared with a series of standards to derive the molecular weight.
1. Definitions
As used herein, the term xe2x80x9cHAPxe2x80x9d refers to the hydrophobically associative polymer of this invention.
As used herein, the term xe2x80x9chydrocarbonxe2x80x9d includes xe2x80x9caliphaticxe2x80x9d, xe2x80x9ccycloaliphaticxe2x80x9d, and xe2x80x9caromaticxe2x80x9d. The terms xe2x80x9caliphaticxe2x80x9d and xe2x80x9ccycloaliphaticxe2x80x9dxe2x80x94unless stated otherwisexe2x80x94are understood as including xe2x80x9calkylxe2x80x9d, xe2x80x9calkenylxe2x80x9d, xe2x80x9calkynylxe2x80x9d, and xe2x80x9ccycloalkylxe2x80x9d. The term xe2x80x9caromaticxe2x80x9dxe2x80x94also unless stated otherwisexe2x80x94is understood as including xe2x80x9carylxe2x80x9d, xe2x80x9caralkylxe2x80x9d, and xe2x80x9calkarylxe2x80x9d.
Hydrocarbon groups are understood as including both nonsubstituted hydrocarbon groups and substituted hydrocarbon groups, with the latter referring to the hydrocarbon portion bearing additional substituents besides the carbon and hydrogen. Correspondingly, aliphatic, cycloaliphatic, and aromatic groups are understood as including both nonsubstituted aliphatic, cycloaliphatic, and aromatic groups and substituted aliphatic, cycloaliphatic, and aromatic groups, with the latter referring to the aliphatic, cycloaliphatic, and aromatic portion bearing additional substituents besides the carbon and hydrogen.
Also as discussed herein, copolymers are understood as including polymers consisting of, or consisting substantially of or consisting essentially of, two different monomeric units. Copolymers are further understood as including polymers incorporating three or more different monomeric units, e.g., terpolymers, etc.
2. Hydrophobic Monomer
The hydrophobic monomers which are useful in this method are those known in the art. They include water-insoluble hydrophobic ethylenically unsaturated monomers, particularly water-insoluble monomers, having hydrophobic groups. The hydrophobic groups include hydrophobic organic groups, such as those having hydrophobicity comparable to one of the following: aliphatic hydrocarbon groups having at least six carbons (preferably from C8 to C22 alkyls and preferably from C6 to C22 cycloalkyls); polynuclear aromatic hydrocarbon groups such as benzyls, substituted benzyls and naphthyls; alkaryls wherein alkyl has one or more carbons; haloalkyls of four or more carbons, preferably perfluoroalkyls; polyalkyleneoxy groups wherein the alkylene is propylene or higher alkylene and there is at least one alkyleneoxy unit per hydrophobic moiety. The preferred hydrophobic groups include those having at least 6 carbons or more per hydrocarbon group, preferably C6 to C22 alkyl groups or those having at least 6 carbons or more per perfluorocarbon group, such as the C6F13-C22F45. Particularly preferred are the C8-C20 alkyl groups.
Suitable hydrocarbon group-containing ethylenically unsaturated monomers include the esters or amides of the C6 and higher alkyl groups.
Particular suitable esters include dodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecyl methacrylate, tetradecyl acrylate, tetradecyl methacrylate, octadecyl acrylate, octadecyl methacrylate, nonyl-xcex1-phenyl acrylate, nonyl-xcex1-phenyl methacrylate, dodecyl-xcex1-phenyl acrylate, and dodecyl-xcex1-phenyl methacrylate.
The C10-C20 alkyl esters of acrylic and methacrylic acid are preferred. Of these, dodecyl acrylate and methacrylate are particularly preferred.
Also the following hydrocarbon group-containing ethylenically unsaturated monomers may be used:
N-alkyl, ethylenically unsaturated amides, such as N-octadecyl acrylamide, N-octadecyl methacrylamide, N,N-dioctyl acrylamide and similar derivatives thereof,
xcex1-olefins, such as 1-octene, 1-decene, 1-dodecene, and 1-hexadecene;
vinyl alkylates wherein the alkyl has at least eight carbons, such as vinyl laurate and vinyl stearate;
vinyl alkyl ethers, such as dodecyl vinyl ether and hexadecyl vinyl ether;
N-vinyl amides, such as N-vinyl lauramide and N-vinyl stearamide; and
alkylstyrenes such as t-butyl styrene.
The hydrophobic monomer is present in an amount up to about 10 mole percent. It is preferred that the hydrophobic monomer be present in an amount from about 0.1 to about 2 mole percent and most preferred that the hydrophobic monomer be present in an amount from about 0.25 to about 1 mole percent. A preferred hydrophobic monomer is lauryl acrylate.
3. Nonionic Hydrophilic Monomers
The nonionic hydrophilic monomers useful in this method are those known in the art. They include nonionic ethylenically unsaturated monomers such as acrylamide; methacrylamide; N-alkylacrylamides, such as N-methylacrylamide; N,N-dialkylacrylamides, such as N,N-dimethylacrylamide; methyl acrylate; methyl methacrylate; acrylonitrile; N-vinyl methylacetamide; N-vinyl methyl formamide; vinyl acetate; N-vinyl pyrrolidone; mixtures of any of the foregoing and the like. Of the foregoing, acrylamide, methacrylamide, and the N-alkylacrylamides are preferred, with acrylamide being particularly preferred.
The nonionic hydrophilic monomer is present in an amount up to about 99 mole percent. It is preferred that the nonionic hydrophilic monomer be present in an amount from about 10 to about 90 mole percent and most preferred that the nonionic hydrophilic monomer be present in an amount from about 30 to about 70 mole percent.
4. Cationic Hydrophilic Monomers
The cationic hydrophilic monomers useful in this method are those known in the art. They include cationic ethylenically unsaturated monomers such as diallyldialkylammonium halides, such as diallyldimethylammonium chloride; acryloxyalkyltrimethylammonium chloride; the (meth)acrylates of dialkylaminoalkyl compounds, and the salts and quaternaries thereof; the N,N-dialkylaminoalkyl(meth)acrylamides, and the salt and quaternaries thereof, such as N,N-dimethylaminoethylacrylamides; (meth)acrylamidopropyltrimethylammonium chloride; and the acid and quaternary salts of N,N-dimethylaminoethylacrylate; N-vinylformamide and the associated hydrolyzate N-vinylamine homopolymers and copolymers; the quaternized N-vinylamine homopolymers and copolymers. The N,N-dialkylaminoalkyl acrylates and methacrylates, and their acid and quaternary salts, are preferred, with the methyl chloride quaternary of N,N-dimethylaminoethylacrylate being particularly preferred.
Further as to the cationic monomers, suitable examples include those of the following general formulae: 
where R1 is hydrogen or methyl, R2 is hydrogen or lower alkyl of C1 to C4, R3 and/or R4 are hydrogen, alkyl of C1 to C12, aryl, or hydroxyethyl, and R2 and R3 or R2 and R4 can be combined to form a cyclic ring containing one of more hetero atoms, Z is the conjugate base of an acid, X is oxygen or xe2x80x94xe2x80x94NR1 wherein R1 is as defined above, and a is an alkylene group of C1 to C12; or 
where R5 and R6 are hydrogen or methyl, R7 is hydrogen or alkyl of C1 to C12, and R8 is hydrogen, alkyl of C1 to C12, benzyl, or hydroxyethyl; and Z is as defined above; or 
where R1, R2 and R3 are each H or C1 to C3 alkyl, and Z is defined above.
The cationic hydrophilic monomer is present in an amount up to about 99 mole percent. It is preferred that the cationic hydrophilic monomer be present in an amount from about 10 to about 90 mole percent and most preferred that the cationic hydrophilic monomer be present in an amount from about 30 to about 70 mole percent.
4. Anionic Hydrophilic Monomers
The anionic hydrophilic monomers useful in this method are those known in the art. They include anionic ethylenically unsaturated monomers such as acrylic acid, methacrylic acid, and their salts; 2-acrylamido-2-methyl-propane sulfonate; sulfoethyl-(meth)acrylate; vinylsulfonic acid; styrene sulfonic acid; and maleic and other dibasic acids and their salts. Acrylic acid, methacrylic acid and their salts are preferred, with the sodium and ammonium salts of acrylic acid being particularly preferred.
The anionic hydrophilic monomer is present in an amount up to about 99 mole percent. It is preferred that the anionic hydrophilic monomer be present in an amount from about 10 to about 90 mole percent and most preferred that the anionic hydrophilic monomer be present in an amount from about 30 to about 70 mole percent.
5. Surfactants
The method relies on the complete solubilization of the water insoluble monomer by means of a dilute solution of a suitable water soluble surfactant. The type and concentration of surfactant are chosen to produce a clear, uniform, homogeneous aqueous dispersion of the hydrophobic monomers in the presence of both non-ionic and anionic water soluble monomers and, in addition, the reaction medium remains a clear, uniform, homogeneous mixture with no phase separation as the reaction proceeds to completion. The micelles formed by the surfactant are small aggregates, consisting of on the order of 50 to 200 molecules. They are stable toward phase separation and effectively disperse the water insoluble monomer on a very fine scale so that the polymerization is effected without the formation of latexes of fine particulates of water insoluble polymer.
The surfactants which may be used in this method may be any surfactant known in the art, such as those disclosed in McCutcheon""s Emulsion Detergents. The surfactants may be one of the water soluble surfactants, such as salts of alkyl sulfates, sulfonates and carboxylates, or alkyl arene sulfates, sulfonates or carboxylates or may be nitro product based surfactants. Preferred surfactants are sodium or potassium salts of decyl sulfate, dodecyl sulfate or tetradecylsulfate. For these ionic surfactants the Kraft point, which is defined as the minimum temperature for micellar formation, must be below the temperature used for the polymerization. Thus, at the conditions of polymerization the desired surfactant will form micelles which solubilize the water insoluble monomer. Nonionic surfactants can also be used for preparing the polymers of this invention. For example, ethoxylated alcohols, ethoxylated alkyl phenols, ethoxylated dialkyl phenols, ethylene oxide-propylene oxide copolymers and polyoxyethylene alkyl ethers and esters can be used. Preferred nonionic surfactants are ethoxylated nonyl phenol with 5 to 20 ethylene oxide units per molecule, ethoxylated nonyl phenol with 5 to 20 ethylene oxide units per molecule, ethoxylated dinonyl phenol containing 5 to 40 ethylene oxide units per molecule and ethoxylated octyl phenol with 5 to 15 ethylene oxide units per molecule. Surfactants which contain both nonionic and anionic functionality, e.g., sulfates of ethoxylated alcohols and alkyl phenols, can also be used.
Combinations of anionic and nonionic surfactants can also be used, as long as the surfactants solubilize the hydrophobic monomer into an aqueous phase containing the water soluble monomers. Thus, the actual concentration of surfactant for a given polymerization will depend on the concentration of oil soluble or hydrophobic monomers employed.
The surfactant should be present in an amount up to about 10 weight percent. It is preferred that the surfactant be present in an amount from about 0.1 to about 5 weight percent and most preferred that the surfactant be present in an amount from about 0.2 to about 2 weight percent. A preferred surfactant is sodium lauryl sulfate.
6. Initiators
Polymerization of the water soluble and water insoluble monomers is effected in an aqueous micellar solution containing a suitable free radical initiator. Examples of suitable water soluble free radical initiators include peroxides, such as hydrogen peroxide, and persulfates, such as sodium, potassium or ammonium persulfate. The concentration of the free radical initiator is about 0.01 to about 0.5 gram per hundred grams of total monomers. Suitable oil soluble initiators are organic peroxides and azo compounds, such as azobisisobutyronitrile. Water soluble redox initiators are preferred, such as potassium persulfate and sodium metabisulfite. Redox initiation involving an oxidant, such as potassium persulfate, and a reductant, such as sodium metabisulfite, can also be used to initiate polymerization, particularly at low temperatures.
Polymerizing at lower temperatures results in the formation of higher molecular weight polymers which are desirable from the standpoint of efficient aqueous viscosification. The polymerization temperature is preferably about 0xc2x0 C. to about 90xc2x0 C., more preferably about 15xc2x0 C. to about 70xc2x0 C.
The initiators may be present in an amount from about 1 to about 100,000 parts per million (ppm). It is preferred that the initiators be present in an amount from about 10 to about 1,000 ppm and it is most preferred that initiators be present in an amount from about 30 to about 300 ppm.
7. Brine Solution
The polyvalent salt is preferably a sulfate or phosphonate such as ammonium, sodium, magnesium or aluminum sulfate or ammonium, sodium or potassium hydrogen phosphate. The concentration of salt in the aqueous salt solution may be up to about 50 weight percent of the total solution.
It is preferred that the polyvalent salt be present in an amount from about 10 to about 30 weight percent and most preferred that the polyvalent salt be present in an amount from about 10 to about 18 weight percent of the total solution.
The monomer solution exerts a hydrophobic effect in aqueous environment. Without being bound by theory, it is believed that the salt plays two rolesxe2x80x94initially the salt solubilizes the monomers into aqueous solution and after polymerization of the monomers into a HAP, the salt precipitates the HAP. The amount of salt needed is directly related to the concentration of the monomer solution. The more concentrated the monomer solution, the more salt is needed.
7. Stabilizer
Stabilizer is crucial to the system since it affects the homogeneity of the dispersion and the appearance thereof. Because of the stabilizer, the dispersion is easier to process and has less tendency to clogging or settling out. The resulting dispersion is stable and without phase separation in storage.
The stabilizers may include any vegetable gum, a polysaccharide, or a cellulose product, as well as their chemically modified derivatives. They can be modified by reacting gum, polysaccharide or cellulose with long chain alkyl group, propylene oxide, ethylene oxide, chloroacetic acid, or N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (Quat 188 from Dow), respectively to obtain hydrophobic, anionic or cationic derivatives. A preferred stabilizer of the invention is a modified guar gum, Galactasol Gum 60F3HDS, from Aqualon Division of Hercules, Inc.
The stabilizer may be present in an amount up to about 10 weight percent of the salt solution. It is preferred that the stabilizer be present in an amount from about 0.5 to about 2 weight percent and most preferred that the stabilizer be present in an amount from about 0.1 to 0.5 weight percent.